UNIVERSITY  OF   CALIFORNIA  PUBLICATIONS 

COLLEGE  OF  AGRICULTURE 

AGRICULTURAL  EXPERIMENT  STATION 

BERKELEY,  CALIFORNIA 


A  COMPARISON  OF  ANNUAL  CROPPING, 

BIENNIAL  CROPPING,  AND  GREEN 

MANURES  ON  THE  YIELD 

OF  WHEAT 


BY 
B.  A.  MADSON 


BULLETIN  No.  270 

August,  1916 


UNIVERSITY  OF  CALIFORNIA  PRESS 

BERKELEY 

1916 


Benjamin  Ide  Wheeler,  President  of  the  University. 
EXPEEIMENT  STATION  STAFF 

HEADS    OF   DIVISIONS 

Thomas  Forsyth  Hunt,  Director. 
Edward  J.  Wickson,  Horticulture  (Emeritus). 

Herbert  J.  Webber,  Director  Citrus  Experiment  Station;  Plant  Breeding. 
Hubert  E.  Van  Norman,  Vice-Director;  Dairy  Management. 
William  A.  Setchell,  Botany. 
Myer  E.  Jaffa,  Nutrition. 

Eobert  H.  Loughridge,  Soil  Chemistry  and  Physics  (Emeritus). 
Charles  W.  Woodworth,  Entomology. 
Ealph  E.  Smith.  Plant  Pathology. 
J.  Eliot  Coit.  Citriculture. 
John  W.  Gilmore,  Agronomy. 
Charles  F.  Shaw,  Soil  Technology. 

John  W.  Gregg,  Landscape  Gardening  and  Floriculture. 
Frederic  T.  Bioletti,  Viticulture  and  Enology. 
Warren  T.  Clarke,  Agricultural  Extension. 
John  S.  Burd,  Agricultural  Chemistry. 
Charles  B.  Lipman,  Soil  Chemistry  and  Bacteriology. 
Clarence  M.  Haring,  Veterinary  Science  and  Bacteriology. 
Ernest  B.  Babcock,  Genetics. 
Gordon  H.  True,  Animal  Husbandry. 
James  T.  Barrett,  Plant  Pathology. 
Fritz  W.  Woll,  Animal  Nutrition. 
A.  V.  Stubenrauch,  Pomology. 
Walter  Mulford,  Forestry. 
W.  P.  Kelley,  Agricultural  Chemistry. 
Elwood  Mead,  Eural  Institutions. 
H.  J.  Quayle,  Entomology. 
J.  B.  Davidson,  Agricultural  Engineering. 
H.  S.  Eeed,  Plant  Physiology. 
D.  T.  Mason,  Forestry. 

William  G.  Hummel,  Agricultural  Education. 
John  E.  Dougherty,  Poultry  Husbandry. 
S.  S.  Eogers,  Olericulture. 
*Frank  Adams,  Irrigation  Investigations. 
David  N.  Morgan,  Assistant  to  the  Director. 
Mrs.  D.  L.  Bunnell,  Librarian. 


division  of  agronomy 

J.  W.  Gilmore  W.  E.  Packard 

P.  B.  Kennedy  G.  W.  Hendry 

E.  L.  Adams  J.  A.  Denny 

B.  A.  Madson  L.  K.  Marshall 


*  In  co-operation  Office  of  Public  Eoads  and  Eural  Engineering,  U.  S.  D.  A. 


A  COMPARISON  OF  ANNUAL  CROPPING,  BIENNIAL 

CROPPING,  AND  GREEN  MANURES  ON  THE 

YIELD  OF  WHEAT* 


By  B.  A.  MADSON 


It  has  been  observed  that  the  productive  power  of  the  arid  and 
semi-arid  soil  of  the  west  is  more  often  limited  because  of  an  insuffi- 
cient supply  of  moisture  or  because  of  improper  physical  and  biological 
conditions  than  because  of  a  lack  of  certain  fertilizing  elements.  This 
is  especially  true  where  dry  farming  is  practiced,  in  which  case  the 
cereals  constitute  the  principal  crop  grown.  In  the  more  humid  sec- 
tions, where  water  is  usually  abundant,  corresponding  defects  in 
physical  and  biological  conditions  may  generally  be  corrected  by  the 
use  of  systems  of  crop  rotation.  Under  arid  conditions  the  develop- 
ment of  a  comprehensive  system  of  crop  rotation  is  rendered  somewhat 
difficult  because  of  the  limited  number  of  crops  adapted  to  these 
conditions.  Some  modification  of  this  character,  however,  is  necessary 
in  the  system  of  grain  farming  in  California,  as  evidenced  by  the  fact 
that  wheat  production  in  the  state  has  decreased  more  than  80  per 
cent  during  the  past  ten  years,  a  condition  which  can  be  attributed 
largely  to  the  deleterious  effects  of  continuous  one-sided  cropping. 

To  overcome  this  deficiency  of  crops,  a  year  of  fallow  and  addition 
of  organic  matter  to  the  soil  by  the  use  of  cover  crops  have  been  ad- 
vocated. The  year  of  fallow  is  recommended  primarily  as  a  moisture- 
conserving  measure,  to  make  possible  an  adequate  supply  of  moisture 
in  the  soil  for  a  maximum  crop  at  all  times.  The  use  of  the  cover 
crop,  on  the  other  hand,  is  recommended  as  a  means  of  maintaining 
the  supply  of  humus  which  is  lost  so  rapidly  by  oxidation  under  con- 
tinuous cultivation  and  cropping.  Humus  appears  to  be  necessary  to 
keep  the  soil  in  good  tilth,  to  stimulate  bacterial  activity  and  to  main- 
tain its  maximum  moisture-holding  capacity.  One  or  both  of  these 
practices,  together  with  proper  cultivation,  have  been  found  under 
many  conditions  not  only  to  aid  materially  in  maintaining  the  pro- 
ductivity of  dry-farm  soils  but  in  many  cases  to  be  absolutely  essential 

*  The  experiment  discussed  in  this  publication  was  outlined  by  and  executed 
under  the  direction  of  Dr.  G.  W.  Shaw,  in  charge  of  the  Agronomy  work  until 
1913.  The  field  work  was  conducted  under  the  supervision  of  Mr.  A.  J.  Gaumnitz, 
in  charge  of  the  experimental  work  at  Davis  during  the  same  period  of  time. 


4  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

to  successful  crop  production.  On  the  sandy  soils  near  Ceres,  in  the 
San  Joaquin  Valley,  Shaw1  found  that  by  the  use  of  the  summer  fallow 
alone  the  yield  of  wheat  could  be  more  than  doubled,  while  by  the  use 
of  green  manure  crops,  combined  with  the  summer  fallow,  the  yield 
was  increased  from  230  to  340  per  cent,  depending  upon  the  amount 
of  organic  matter  added.  Necessarily,  however,  the  effect  of  these 
treatments  will  vary  not  only  with  the  total  precipitation  and  its 
seasonal  distribution  but  more  particularly  with  the  type  and  char- 
acter of  the  soil. 

In  order  to  secure  some  information  as  to  the  value  of  these  treat- 
ments under  Sacramento  Valley  conditions,  a  biennial  cropping  ex- 
periment was  begun  in  1907  on  the  University  Farm  at  Davis,  a  portion 
of  which  was  previously  discussed  by  Shaw  in  the  bulletin  above  cited. 
This  project  was  designed  to  show  the  effects  of  fallow  and  of  various 
green  manure  crops  in  combination  with  the  fallow,  as  compared  with 
continuous  cropping  on  the  yield  of  wheat.  The  results  obtained  in 
this  investigation  since  the  publication  of  Professor  Shaw's  bulletin 
are  presented  in  this  bulletin,  with  such  discussions  as  these  may 
suggest. 

Climate. — The  climate  at  Davis  is  usually  classed  as  semi-arid. 
The  normal  precipitation  is  approximately  17.32  inches,  the  greater 
portion  of  which  falls  during  the  winter  months,  while  the  months  of 
June  to  September  are  generally  absolutely  rainless.  There  is,  how- 
ever, a  very  wide  variation  in  the  seasonal  precipitation,  as  indicated 
by  the  subjoined  table.  This  fact  and  the  frequent  occurrence  of  hot 
north  winds  during  the  spring  and  summer  months  render  moisture- 
conserving  measures  imperative. 

TABLE  I 

Eainfall  at  Davis 

Seasons,  1907-08    1908-09    1909-10    1910-11    1911-12    1912-13  1913-14 
Inches  13.16       22.48       11.35       23.18         9.41         8.84       28.70 

Soil. — The  soil  type  upon  which  this  experiment  was  undertaken 
is  technically  known  as  Davis  silt  loam.  The  surface  soil  is  a  rather 
heavy  silt  loam  varying  in  depth  from  four  to  five  feet.  It  is,  how- 
ever, in  fair  physical  condition,  is  relatively  easy  to  work,  and  has  a 
maximum  water-holding  capacity  of  approximately  30  per  cent,  ac- 
cording to  field  determinations.  This  surface  soil  is  underlaid  by  a 
layer  of  sand  six  to  eight  inches  in  thickness  and  this  in  turn  under- 
laid by  a  heavier  clay  loam. 


i  Calif.  Bulletin  No.  211,  p.  267. 


EFFECT  OF  CROPPING  SYSTEMS  ON  WHEAT  O 

The  project  consisted  of  fourteen  one-tenth  acre  plats  quite  uni- 
form in  character  and  included  five  trials  with  various  green  manure 
crops  as  compared  with  bare  fallow  and  with  continuous  cropping. 
Each  test  was  made  in  duplicate,  so  that  of  the  biennial  cropped  plats 
one  plat  out  of  each  series  was  cropped  to  wheat  every  year.  During 
the  summer  of  1907  all  plats  were  fallowed  in  order  to  disintegrate 
the  plow  sole  and  put  the  soil  in  as  good  physical  condition  as  possible. 
This  was  deemed  advisable  inasmuch  as  the  field  had  been  cropped  to 
grain  for  a  number  of  years  prior  to  its  being  used  for  experimental 
purposes. 

Treatment  of  Plats. — During  the  subsequent  year  all  plats  received 
the  same  cultural  treatment  as  far  as  conditions  would  permit.  Plow- 
ing was  done  in  the  late  fall  or  early  winter,  as  soon  as  the  rain  had 
sufficiently  moistened  the  ground.  The  surface  was  then  worked  down 
to  a  good  seed  bed  and  the  wheat  and  the  green  manure  crop  seeded 
with  a  drill.  The  fallow  plats  were  allowed  to  lie  in  the  rough  con- 
dition until  spring,  when  the  weed  growth  was  destroyed  and  the 
surface  worked  down  to  an  even  mulch;  this  mulch  was  maintained 
throughout  the  summer  by  an  occasional  cultivation  with  either  a 
harrow  or  a  disc.  On  the  green  manure  plats  the  cover  crop  was 
turned  under  in  the  spring,  after  which  the  surface  was  worked  down 
to  a  mulch;  this  mulch  was  maintained  throughout  the  summer  in 
exactly  the  same  manner  as  on  the  fallow  plats,  with  one  exception. 
Plats  Nos.  38  and  39,  upon  which  horse  beans  were  grown  as  a  cover 
crop,  were  plowed  in  the  spring,  worked  down  and  planted  to  Kaffir 
corn  during  a  part  of  the  experiment. 

When  the  wheat  crop  was  removed  from  the  plats  in  the  summer 
the  stubble  was  immediately  disced,  the  mulch  thus  formed  aiding 
materially  in  checking  the  loss  of  moisture  from  the  soil  by  direct 
evaporation.  The  treatment  of  the  various  plats  and  the  yields  ob- 
tained are  given  in  Table  II. 

In  comparing  the  data  presented  in  Table  II  it  will  be  observed 
that  the  average  yield  of  the  two  continuously  cropped  plats,  Nos.  30 
and  37,  namely,  21.75  bushels  per  acre,  is  slightly  higher  than  the 
average  of  any  of  the  biennial  cropped  plats.  Of  the  biennial  cropped 
plats,  Nos.  33  and  34,  on  which  horse  beans  and  fenugreek  were  grown 
as  a  cover  crop,  gave  the  highest  returns.  In  all  fairness,  however, 
it  must  be  said  that  the  horse  beans  failed  to  produce  much  growth, 
so  that  their  effect  as  a  green  manure  crop  was  practically  nothing. 
The  fenugreek,  however,  made  a  fair  growth,  but  had  occasion  to 
influence  but  one  of  the  six  wheat  crops.  In  reality,  therefore,  the 
treatment  of  these  plats  prior  to  the  use  of  the  fenugreek  was  practi- 


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EFFECT  OF  CROPPING  SYSTEMS  ON  WHEAT  7 

cally  the  same  as  on  the  bare  fallow.  On  plats  Nos.  38  and  39  the 
horse  beans  were  likewise  a  failure. 

Perhaps  the  most  striking  fact  revealed  by  the  data  in  Table  II 
is  the  rapid  decrease  in  yield  of  the  continuously  cropped  plats  during 
the  progress  of  the  experiment.  In  the  case  of  the  biennial  cropped 
plats  there  appears  to  be  no  consistent  change  in  productivity^  with 
the  exception  of  plats  Nos.  40  and  41,  upon  which  rye  and  vetch  were 
employed  as  a  cover  crop.  In  fact,  it  is  evident  that  had  the  experi- 
ment continued  a  few  years  longer  all  the  biennial  cropped  plats,  with 
the  possible  exception  noted,  would  have  surpassed  in  yield  the  con- 
tinuously cropped  plats. 

It  must  also  be  remembered  that  all  the  plats  were  fallowed  during 
the  summer  of  1907,  prior  to  the  beginning  of  the  experiment,  so  that 
the  condition  on  plats  Nos.  30  and  37,  for  the  first  season  at  least,  was 
identical  with  that  of  the  biennially  cropped  plats.  The  results  clearly 
indicate  that  the  year  of  fallow  very  markedly  affected  the  growth 
on  the  continuously  cropped  plats  for  at  least  two  seasons.  This  is 
especially  significant  considering  the  short  duration  of  the  experiment. 
Furthermore,  one  plat  out  of  each  series  of  the  biennial  cropped  plats 
was  not  cropped  for  the  two  seasons,  1906-07  and  1907-08,  a  condition 
which  might  tend  to  vitiate  the  results  somewhat,  though  the  effect, 


TABLE  III 

Eesults  of  the 

Last  Four  Years  of  the  Biennial  Cropping  Experiment 

Plat 

No. 

1909-10 

1910-11 

1911-12 

1912-13 

Total 

4  yr. 
Yield  per 
acre,  bu. 

Av.  annual   Grand 
yield  per    average, 
acre,  bu.         bu. 

30  Ck. 

21.58 

10.33 

10.83 

3.17 

45.91 

11.48 

11.48 

31 

28.00 

Fallow 

44.83 

Fallow 

72.83 

18.21 

►       17.67 

32 

Fallow 

24.75 

Fallow 

43.83 

68.58 

17.14 

33 

34 

Horse  beans 
28.91 

34.83 
Horse  beans 

Fenugreek 
41.33 

40.67 
Fenugreek 

75.50 
70.56 

18.87 
17.56 

1       18.21 

35 

Field  peas 

34.33 

Field  peas 

31.42 

65.75 

16.44 

I       16.71 

36 

29.25 

Field  peas 

37.66 

Field  peas 

67.98 

16.98 

37  Ck 

22.41 

11.00 

6.66 

5.08 

43.18 

11.29 

11.29 

38 

Horse  beans 

j 

' 

Kafir 

28.58 

Horse  beans 

28.58 

57.16 

14.29 

>       16.83 

39 

31.83 

Horse  beans 

Kafir 

45.66 

Horse  beans 

77.49 

19.37 

40 

Rye  &  vetch 

29.00 

Rye  &  vetch 

9.07 

38.17 

9.54 

>       10.34 

41 

32.08 

Rye  &  vetch 

12.50 

Rye  &  vetch 

44.58 

11.14 

42 

Burr  clover 

26.16 

Burr  clover 

23.17 

49.83 

12.46 

1 

43 

41.41 

Burr  clover 

39.50 

Burr  clover 

79.91 

19.98 

{       16.22 

8  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

if  any,  is  less  apparent.  Again,  on  the  green  manure  plats  the  treat- 
ment in  some  cases  did  not  become  effective  until  the  third  year,  so 
that  only  the  last  four  years  show  a  true  comparison  of  the  various 
treatments.  On  the  whole,  therefore,  it  would  probably  be  better  to 
regard  the  first  two  seasons '  results  as  preliminary  and  to  include  only 
the  last  four  years 7  results  in  comparing  the  merits  of  the  various 
treatments.    The  yields  considered  on  this  basis  are  given  in  Table  III. 

The  results  of  the  last  four  years  have  been  decidedly  in  favor  of 
biennial  cropping,  with  the  exception  of  plats  Nos.  40  and  41,  on  which 
rye  and  vetch  were  employed  as  a  cover  crop.  The  difference  in  yield, 
however,  between  the  continuously  cropped  plats  and  the  biennially 
cropped  plats  is  too  great  to  be  attributed  to  any  other  factor  than  the 
effect  of  the  treatment  given.  Unfortunately  no  determinations  were 
made  on  the  green  manure  plats  to  ascertain  whether  or  not  there 
was  any  relation  between  the  total  weight  of  organic  matter  added  to 
the  soil  and  the  yield  produced.  Attention  must  be  called  to  the  fact, 
however,  that  the  green  manure  plats,  Nos.  40  and  41,  which  gave  the 
lowest  average  yield,  not  only  for  the  last  four  years  but  throughout 
the  experiment  were  the  only  ones  upon  which  a  cereal  was  employed 
as  a  cover  crop.  It  is  quite  probable  that  the  total  organic  matter 
added  was  greater  when  rye  was  used  as  a  part  of  the  cover  crop  than 
when  a  legume  alone  was  used.  This  would  seem  to  indicate  either 
that  the  growth  of  a  larger  cover  crop  tended  to  reduce  correspond- 
ingly the  water  content  of  the  soil,  thereby  affecting  the  yield  of  the 
following  crop,  or  that  the  cereal  (rye)  exerted  some  influence  on  the 
soil  which  affected  the  growth  of  the  succeeding  crop  unfavorably. 
On  the  whole,  in  comparing  the  effect  of  the  various  cover  crops  with 
bare  fallow  the  results  would  indicate  that  the  cover  crop  was  harmful 
rather  than  beneficial.  However,  plats  Nos.  33  and  34,  upon  which 
horse  beans  and  fenugreek  were  grown  as  cover  crops,  the  former  being 
almost  a  total  failure,  gave  a  slightly  higher  yield  than  the  bare  fallow 
plats.  Even  plats  Nos.  38  and  39,  upon  which  the  cover  crop  of  horse 
beans  was  followed  by  Kafir  corn  during  the  first  four  years,  gave  as 
large  a  yield  of  wheat  throughout  the  experiment  as  did  the  field  peas 
and  bur  clover  plats.  "While  the  Kafir  did  not  mature  in  most  cases, 
the  yield  of  forage  varied  from  four  to  eight  tons  per  acre,  the  growth 
of  which  must  have  caused  a  considerably  greater  draft  upon  the 
moisture  supply  of  the  soil  than  did  the  cover  crops.  Furthermore, 
the  Kafir  and  other  sorghums  are  generally  considered  to  be  "hard" 
on  the  soil,  greatly  reducing  the  yield  of  the  following  cereal  crops. 

The  rapid  and  consistent  decrease  in  yield  of  both  the  continuously 
cropped  plats  is  striking.    At  first  it  would  appear  that  this  decrease 


EFFECT  OF  CROPPING  SYSTEMS  ON  WHEAT  9 

might  be  accounted  for  by  an  insufficient  supply  of  moisture.  For 
the  last  two  crops  at  least  this  is  doubtless  true,  as  the  rainfall  was 
very  low,  the  combined  precipitation  for  the  two  seasons  being  only 
18.25  inches.  On  the  whole,  however,  there  seems  to  be  no  close  cor- 
relation between  the  average  yield  of  the  continuously  cropped  plats 


YEAE.S 
W-08      1908-09      1909-10        1910-11 


FIG.  1_ CURVES  SHOWING    THE  fcELATIOM  5ETWEE/1 
THE  RAfMFALL  AMD  THE  YIELDS  Oh  THE 
PLATS   CROPPED  TO  WHEAT  CO/NTIMUOU5LY 


and  the  seasonal  precipitation,  as  is  shown  by  figure  1,  the  yield  de- 
creasing continually  while  the  precipitation  was  decidedly  variable. 
It  is  further  worthy  of  note  that  in  1913,  the  second  of  two  dry  years, 
the  yield  on  plat  No.  32,  which  was  fallowed  the  previous  season,  was 
43.83  bushels  of  wheat  per  acre,  while  plat  No.  33,  to  which  a  cover 


10  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

crop  of  fenugreek  had  been  added  the  previous  season,  yielded  40.67 
bushels  of  wheat  per  acre.  The  results  obtained  the  succeeding  season 
(1914)  further  strengthened  the  belief  that  water  alone  was  not  the 
limiting  factor.  While  the  experiment  was  technically  closed  at  the 
end  of  the  1913  season,  all  the  plats,  with  the  exception  of  No.  32,  were 
cropped  to  some  cereal  the  next  year,  the  results  of  which  are  given  in 
Table  IV.  Plats  Nos.  30  and  31  were  both  planted  to  the  same  variety 
of  wheat.  It  will  be  noted  that  the  yield  of  plat  No.  30,  which  has  been 
cropped  to  wheat  continuously,  was  only  11.17  bushels  per  acre  in  spite 
of  the  fact  that  the  seasonal  precipitation  was  28.70  inches. 


TABLE  IV 

Yield  of  Cereals  on  the  Plats  of  the  Biennial  Cropping  Experiment, 

Season  of  1914 

Yield 


Plat 
No. 

Treatment,  1913 

Crop  grown,  1914 

per  acre, 
bu. 

30 

Wheat 

Bobs  Wheat 

11.17 

31 

Fallow 

Bobs  Wheat 

25.42 

32 

Wheat 

Fallow 

33 

Wheat 

Beldi  Barley  190 

58.20 

34 

Fenugreek 

Beldi  Barley  190 

65.20 

35 

Wheat 

Imp.  Beldi  Bar.  1601 

53.80 

36 

Field  Peas 

Chevalier  Bar.  5865 

65.60 

37 

Wheat 

Chevalier  Bar.  5865 

29.40 

38 

Wheat 

Chevalier  Bar.  5865 

52.80 

39 

Horse  Beans 

Burt  Oats  293 

40.00 

40 

Wheat 

Burt  Oats  293 

44.69 

41 

Eye  and  Vetch 

Burt  Oats  293 

47.66 

42 

Wheat 

white  Aust.  Wh.  12113 

28.16 

43 

Burr  Clover 

White  Aust.  Wh.  12113 

24.37 

Plat  No.  31,  which  had  been  fallowed  the  previous  season,  yielded 
25.42  bushels  of  wheat  per  acre.  The  other  plats  in  the  experiments 
were  cropped  to  various  cereals,  so  that  an  exact  comparison  cannot 
be  made.  The  results  on  the  other  continuously  cropped  plats  and  the 
two  adjoining  plats,  Nos.  36  and  38,  which  were  seeded  to  Chevalier 
barley,  are  also  of  interest.  Plat  No.  37,  which  had  been  continuously 
cropped  to  wheat,  yielded  only  39.4  bushels  of  barley  per  acre.  Plat 
No.  38,  cropped  to  wheat  the  previous  season,  which  was  preceded  by 
a  cover  crop  of  horse  beans,  yielded  52.8  bushels  per  acre,  and  plat 
No.  36,  upon  which  had  been  grown  a  cover  crop  of  field  peas  in  1913, 
yielded  65.6  bushels  of  barley  per  acre.  It  does  not  seem  probable 
that  in  either  instance  the  difference  in  yield  could  be  attributed  to  a 


EFFECT  OF  CROPPING  SYSTEMS  ON  WHEAT  11 

difference  in  moisture  supply,  as  all  plats  were  abundantly  supplied 
with  moisture  throughout  the  growing  season.  In  fact,  the  heavy 
spring  rains  kept  the  soil  nearly  saturated  until  the  crop  was  fully 
headed. 

From  the  data  obtained  it  would  certainly  appear  that  some  factor 
other  than  the  lack  of  moisture  was  responsible  for  the  decline  in  yield 
under  continuous  cropping.  Considering  the  results  obtained  on  the 
plats  in  which  rye  was  used  as  a  part  of  the  cover  crop,  it  would  appear 
that  the  cereal  exerted  some  unfavorable  influence  upon  the  succeeding 
grain  crop.  Whether  this  condition  is  due  to  some  toxic  substance 
left  in  the  soil,  to  the  development  of  fungi,  as  maintained  by  Bolley, 
or  to  some  effect  of  the  fibrous  root  system  on  the  physical,  chemical 
or  biological  condition  of  the  soil  is  still  undetermined.  The  results, 
however,  would  suggest  that  some  effect  of  this  character  was  the  real 
limiting  factor.  The  fact  that  most  of  the  plats  upon  which  a  legum- 
inous cover  crop  had  been  grown  gave  a  lower  yield  than  the  bare 
fallow  plats  might  be  explained  on  the  basis  of  moisture,  the  cover 
crop  using  a  portion  of  the  moisture  which  might  otherwise  have 
served  to  supply  the  wheat  crop.  This  explanation  seems  plausible, 
since  the  difference  in  yield  during  seasons  of  high  rainfall  was  very 
slight,  the  greatest  difference  occurring  during  the  drier  seasons.  It 
would  seem,  therefore,  that  while  the  addition  of  organic  matter  may 
be  of  value,  its  beneficial  effect  is  not  sufficient  to  compensate  for  the 
water  used  in  its  growth,  nor  does  the  soil  appear  to  be  seriously 
lacking  in  any  constituent  which  the  cover  crop  might  add. 

From  an  economic  point  of  view,  the  bare  fallow  unquestionably 
produced  the  greatest  net  returns  per  acre.  The  cost  of  maintaining 
a  good  summer  fallow,  including  plowing  and  the  necessary  cultiva- 
tion, is  usually  slightly  less  than  the  cost  of  producing  a  crop  of  wheat. 
The  annual  increase  in  yield  of  6.29  bushels  per  acre,  which  was  ob- 
tained from  the  fallow  plats,  is  therefore  largely  clear  gain.  In  other 
words,  to  be  economically  a  success,  the  fallow  plats  would  have  to 
produce  only  twice  as  large  yields  every  alternate  year  as  was  pro- 
duced by  the  continuous  cropped  plats  annually,  whereas  the  actual 
average  production  of  the  fallow  plats  every  two  years  was  35.35 
bushels  per  acre,  as  compared  with  11.38  bushels  per  acre,  which  was 
the  annual  production  of  the  plats  cropped  continuously. 

In  the  case  of  the  green  manure  plats,  while  the  yields  were  consid- 
erably larger  than  those  obtained  under  continuous  cropping,  they 
were,  on  the  whole,  somewhat  lower  than  the  yield  obtained  on  the 
fallow  plats.  Furthermore,  the  cost  of  producing  and  handling  the 
green  manure  crop  is  at  least  50  per  cent  greater  than  the  cost  of 


12  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

maintaining  the  fallow,  including  as  it  does  the  cost  of  putting  in  the 
crops,  the  cost  of  the  seed  and  additional  plowing  in  the  spring,  be- 
sides the  same  summer  cultivation  that  is  given  to  the  fallow.  On  the 
whole,  therefore,  the  actual  economic  returns  attending  the  use  of  a 
green  manure  crop  is  but  slightly  greater  than  those  obtained  under  a 
system  of  continuous  cropping. 

EFFECTS  ON  THE  SOIL 

It  is  usually  maintained  that  the  addition  of  organic  matter  to  the 
soil  by  the  use  of  green  manure  crops  will  aid  in  increasing  its  humus 
content.  In  humid  sections  this  is  true,  and  experiments  have  shown 
that  the  plowing  in  of  a  cover  crop  has  increased  the  humus  content 
in  some  cases  1  per  cent.  Under  arid  conditions,  however,  the  increase 
in  humus  content  by  the  use  of  a  cover  crop  has  been  found  in  most 
instances  to  be  very  slight.  As  has  been  pointed  out  by  Scofield, 
under  arid  conditions  the  low  moisture  content  of  the  surface  soil, 
together  with  high  temperature  and  high  degree  of  aeration,  tends  to 
stimulate  direct  oxidation,  rather  than  humification,  so  that  in  a  short 
time  the  larger  proportion  of  the  organic  matter  may  be  lost  without 
adding  materially  to  the  humus  content  of  the  soil.  Hilgard  also 
states  that  "in  the  absence  of  a  sufficient  degree  of  moisture  to  co- 
operate with  the  agencies  of  humification  the  final  results  in  the  soil 
is  practically  the  same  as  in  the  'fire  fanging'  of  dung.  The  organic 
matter  is  almost  wholly  destroyed  by  direct  oxidation  with  or  without 
the  aid  of  minute  organisms,  leaving  essentially  only  the  ash  behind  to 
be  reincorporated  with  the  soil." 

Unfortunately  no  systematic  studies  were  made  to  determine  the 
effect  of  the  various  treatments  upon  the  soil  in  the  experiments  at 
Davis.  A  few  tests  were  made  in  the  spring  of  1913  by  Mr.  S.  E. 
Ooodall,  at  that  time  a  senior  student  in  the  department  of  agriculture, 
with  a  view  to  determining  the  effect  of  the  various  treatments  on  the 
humus  content  of  the  soil,  as  well  as  on  the  nitrogen  content  of  the 
humus.    The  results  thus  obtained  are  given  in  Table  V. 

The  soil  samples  upon  which  these  determinations  were  made  were 
taken  in  January,  about  ten  months  after  the  last  cover  crop  had  been 
plowed  in.  The  results  indicate  that  no  increase  in  humus  content 
occurred  following  the  application  of  the  green  manure  crop.  While 
a  variation  of  .28  per  cent  of  humus  was  obtained  in  the  first  foot,  both 
extremes  occurred  on  plats  to  which  the  last  cover  crop  had  been  added 
nearly  two  years  previous.  The  difference  in  the  average  humus  con- 
tent for  the  various  treatments  is  too  slight  to  be  significant.  The 
fact  that  the  humus  content  of  the  first  foot  is  slightly  less  on  the 


EFFECT  OF  CROPPING  SYSTEMS  ON  WHEAT  13 


1913 


TABLE  V 

Humus  and 

Humu 

s  Nitrogen  Content  of 

Soils,  January, 

Plat 

No. 

Per 

cent  of  H 

A 

umus 

Per  cent  Nitrogen  in  Humus 

A 

1st  ft. 

2nd  ft. 

3rd  ft. 

1st  ft. 

2nd  ft. 

3rd  ft. 

30 

1.12 

.86 

.62 

15.0 

11.2 

19.4 

31 

1.02 

.90 

.54 

8.5 

8.5 

13.5 

32 

•  .98 

.90 

.54 

10.6 

10.6 

14.7 

33 

1.10 

.90 

.54 

9.5 

7.5 

10.4 

34 

.94 

.82 

.52 

8.5 

9.8 

10.4 

35 

1.06 

.88 

.72 

9.4 

11.2 

12.2 

36 

.94 

.80 

.60 

10.1 

9.8 

10.7 

37 

1.06 

.80 

.64 

8.0 

9.9 

11.7 

38 

1.14 

.94 

.70 

10.3 

10.8 

13.4 

39 

1.18 

1.02 

.62 

9.9 

10.5 

16.4 

40 

1.18 

.90 

.62 

10.2 

8.9 

9.6 

41 

1.10 

.96 

.66 

9.5 

7.3 

10.1 

42 

1.14 

.70 

.54 

8.8 

10.0 

12.2 

43 

1.22 

.74 

.56 

8.4 

8.9 

8.6 

Av.  of  continuously- 
cropped  plats, 
Av.  of  fallow  plats, 

1.09 
1.00 

.83 
.90 

.63 
.54 

11.5 
9.5 

10.5 
9.5 

15.5 
14.1 

Av.  of  green  manure 
plats, 

1.10 

.86 

.61 

9.4 

9.5 

11.4 

fallow  plats  than  on  the  other  plats  corroborates  the  usual  observations 
as  to  the  effect  of  summer  cultivation  on  the  oxidation  of  the  humus. 

In  the  nitrogen  content  of  the  humus,  it  is  not  clear  just  why  the 
humus  in  the  soil  of  the  continuously  cropped  plats  should  be  higher 
in  nitrogen  than  that  of  the  other  plats.  The  most  probable  expla- 
nation would  be  that  less  of  the  organic  matter  left  in  the  soil  as  wheat 
roots  was  lost  by  direct  oxidation  than  in  the  case  of  that  applied  as 
cover  crops.  In  the  latter  case,  in  the  process  of  oxidation  it  is  quite 
likely  that  a  large  portion  of  the  nitrogen  was  lost  as  well.  Another 
possibility  that  suggests  itself  is  that  a  more  rapid  rate  of  nitrification 
occurred  when  the  green  material  had  been  added  than  on  land  that 
had  been  cropped,  so  that  a  larger  portion  of  the  nitrogen  was  changed 
to  the  nitrate  form.  In  the  absence  of  nitrate  determinations,  how- 
ever, this  can  only  be  assumed. 

From  the  results  obtained  in  this  experiment  it  would  appear  that 
soils  such  as  those  at  Davis  contain  sufficient  organic  matter  to  meet 
the  demands  of  a  normal  crop.  While  the  addition  of  organic  matter 
by  the  use  of  a  cover  crop  may  tend  to  stimulate  bacterial  activity  and 
the  liberation  of  plant  food,  the  benefit  thus  derived  is  not  sufficient 
to  counterbalance  the  draught  made  upon  the  soil  moisture  by  the 
growth  of  the  crop.     Furthermore,  because  of  the  rapid  oxidation 


14  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

which  takes  place  in  the  soil  the  cover  crops  did  not  increase  the  humus 
content,  but  were  entirely  lost  before  the  next  wheat  crop  was  grown. 

On  the  other  hand,  the  bare  fallow  greatly  stimulated  the  crop- 
producing  power  of  the  soil,  though  it  is  evident  that  if  long  continued 
the  humus  content  will  be  seriously  depleted.  It  will  doubtless,  there- 
fore, eventually  be  necessary  to  add  organic  matter  in  some  form  if 
the  crop-producing  power  of  these  soils  is  to  be  permanently  main- 
tained. It  would  also  appear  that  there  was  considerable  difference  in 
the  comparative  value  of  the  various  crops  for  green  manure  purposes, 
though  the  exact  reason  for  this  is  not  clear. 

Again,  while  the  highest  economic  returns  were  obtained  from  the 
bare  fallow,  it  does  not  hold  that  biennial  cropping  as  practiced  in 
this  experiment  is  necessarily  productive  of  the  greatest  returns.  It 
is  quite  likely  that  from  an  economic  point  of  view  the  use  of  the  fallow 
every  third  or  even  every  fourth  year  would  give  larger  total  returns 
over  a  long  period  of  time  than  biennial  cropping.  As  an  integral 
part  of  a  dry-farm  rotation,  however,  its  value  can  not  be  questioned. 

CONCLUSIONS 

1.  The  marked  decline  in  wheat  production  in  California  has  been 
caused  by  the  deleterious  effects  of  continuous  one-sided  cropping, 
together  with  inadequate  cultivation. 

2.  Under  a  system  of  continuous  cropping  to  wheat  the  yield  de- 
creases very  rapidly  to  a  point  below  profitable  production. 

3.  The  year  of  fallow  is  one  of  the  most  effective  means  of  retaining 
the  productive  power  of  semi-arid  soils. 

4.  The  use  of  green  manure  crops  increases  the  productivity  of  the 
soil,  but  not  to  the  same  extent  as  does  the  bare  fallow. 

5.  There  appears  to  be  a  decided  difference  in  the  effect  of  the 
various  cover  crops.  Apparently  a  cereal  should  not  be  used  as  a  cover 
crop  in  a  cereal  rotation  on  soils  such  as  those  on  the  University 
Farm  at  Davis. 

6.  The  organic  matter  added  to  the  soil  by  the  cover  crop  appears 
to  be  practically  lost  by  oxidation  the  following  summer. 

7.  The  frequent  use  of  the  fallow  will  probably  hasten  the  depletion 
of  the  humus  content  of  the  soil,  even  though  it  greatly  increases  its 
productive  power. 

8.  The  use  of  cover  crops,  even  if  they  be  legumes,  does  not  seem 
to  increase  the  content  of  humus  or  of  humus  nitrogen  in  the  soil  to 
any  appreciable  extent;  the  favorable  effects  of  cover  crops  that  are 
frequently  observed  must,  therefore,  be  attributed  to  other  causes  than 
an  increase  of  the  humus  in  the  soil. 


STATION   PUBLICATIONS   AVAILABLE   FOE   FREE    DISTRIBUTION 


REPORTS 

1897.      Resistant  Vines,   their   Selection,  Adaptation,   and   Grafting.      Appendix  to  Viticultural 
Report  for  1896. 

1902.  Report  of  the  Agricultural  Experiment  Station  for   1898-1901. 

1903.  Report  of  the  Agricultural  Experiment  Station  for   1901-03. 

1904.  Twenty-second  Report  of  the  Agricultural  Experiment  Station  for   1903-04. 

1914.  Report  of  the  College  of  Agriculture  and  the  Agricultural   Experiment   Station,   July, 

1913-June,   1914. 

1915.  Report  of  the  College  of  Agriculture   and  the  Agricultural  Experiment   Station,   July, 

1914-June,   1915. 


No. 
168. 

169. 

178. 
184. 

185. 

195. 
207. 
208. 
212. 
213. 
216. 


225. 
227. 
230. 
241. 
242. 
246. 
248. 

249. 
250. 


Observations  on  Some  Vine  Diseases 
in   Sonoma  County. 

Tolerance  of  the  Sugar  Beet  for  Alkali. 

Mosquito  Control. 

Report  of  the  Plant  Pathologist  to 
July   1,    1906. 

Report  of  Progress  in  Cereal  Investi- 
gations. 

The  California   Grape  Root-worm. 

The  Control  of  the  Argentine  Ant. 

The  Late  Blight  of  Celery. 

California  White  Wheats. 

The   Principles  of  Wine-making. 

A  Progress  Report  Upon  Soil  and  Cli- 
matic Factors  Influencing  the  Com- 
position of  Wheat. 

Tolerance  of  Eucalyptus  for  Alkali. 

Grape  Vinegar. 

Enological   Investigations. 

Vine  Pruning:  in  California,  Part  I. 

Humus   in   California   Soils. 

Vine   Pruning  in   California,   Part  II. 

The  Economic  Value  of  Pacific  Coast 
Kelps. 

Stock-Poisoning  Plants  of  California. 

The  Loquat. 


BULLETINS 
No. 
251. 


252. 
253. 

254. 
255. 
256. 
257. 
261. 


263. 
265. 
266. 

267. 
268. 
269. 
270. 


271. 


Utilization  of  the  Nitrogen  and  Organic 
Matter  in  Septic  and  Imhoff  Tank 
Sludges. 

Deterioration  of  Lumber. 

Irrigation  and  Soil  Conditions  in  the 
Sierra   Nevada   Foothills,    California. 

The  Avocado  in  California. 

The  Citricola  Scale. 

Value  of  Barlev  for  Cows  Fed  Alfalfa. 

New  Dosage  Tables. 

Melaxuma  of  the  Walnut,  "Juglans 
regia." 

Citrus  Diseases  of  Florida  and  Cuba 
Compared  with  Those  of  California. 

Size  Grade  for  Ripe  Olives. 

Cottony  Rot  of  Lemons  in  California. 

A  Spotting  of  Citrus  Fruits  Due  to  the 
Action  of  Oil  Liberated  from  the  Rind. 

Experiments  with  Stocks  for  Citrus. 

Growing  and  Grafting  Olive  Seedlings. 

Phenolic  Insecticides  and  Fungicides. 

A  Comparison  of  Annual  Cropping, 
Biennial  Cropping,  and  Green  Ma- 
nures on  the  Yield  of  Wheat. 

Feeding  Dairy  Calves  in  California. 


CIRCULARS 

No.  No. 

65.   The  California   Insecticide  Law.  134. 

69.  The    Extermination    of    Morning-Glory.  135. 

70.  Observations    on    the    Status    of    Corn  136. 

Growing  in    California.  13  7. 

76.   Hot   Room   Callusing.  138. 

80.   Boys'   and  Girls'   Clubs.  139. 

82.  The     Common     Ground     Squirrels     of 

California. 

83.  Potato  Growing  Clubs.  140. 

106.  Directions  for  Using  Anti-Hog  Cholera 

Serum. 

107.  Spraying  Walnut  Trees  for  Blight  and  141. 

Aphis    Control. 

108.  Grape  Juice.  142. 

109.  Community  or   Local  Extension   Work 

by  the  High  School  Agricultural  De-  143. 
partment. 

113.  Correspondence  Courses  in  Agriculture.  144. 

114.  Increasing  the  Duty  of  Water.  145. 

115.  Grafting  Vinifera  Vineyards. 

117.  The    Selection    and    Cost    of    a    Small  146. 

Pumping  Plant. 

118.  The  Countv  Farm  Bureau.  147. 
121.    Some    Things    the    Prospective    Settler  148. 

Should  Know.  149. 

124.   Alfalfa   Silage  for  Fattening  Steers.  150. 

126.  Spraying  for  the  Grape  Leaf  Hopper.  151. 

127.  House  Fumigation.  152. 

128.  Insecticide  Formulas. 

129.  The  Control  of  Citrus  Insects.  153. 

130.  Cabbage   Growing  in   California. 

131.  Spraying  for  Control  of  Walnut  Aphis.  154. 

132.  When      to      Vaccinate      against      Hog 

Cholera.  155. 
13  3.   County  Farm  Adviser. 


Control  of  Raisin   Insects. 

Official  Tests  of  Dairy  Cows. 

Melilotus  Indica. 

Wood  Decay  in  Orchard  Trees. 

The  Silo  in  California  Agriculture. 

The  Generation  of  Hydrocyanic  Acid 
Gas  in  Fumigation  by  Portable  Ma- 
chines. 

The  Practical  Application  of  Improved 
Methods -of  Fermentation  in  Califor- 
nia Wineries  during  1913  and  1914. 

Standard  Insecticides  and  Fungicides 
versus   Secret  Preparations. 

Practical  and  Inexpensive  Poultry  Ap 
pliances. 

Control  of  Grasshoppers  in  Imperial 
Valley. 

Oidium  or  Powdery  Mildew  of  the  Vine. 

Suggestions  to  Poultrymen  concerning 
Chicken  Pox. 

Jellies  and  Marmalades  from  Citrus 
Fruits. 

Tomato  Growing  in  California 

"Lungworms" 

Lawn  Making  in  California. 

Round  Worms  in  Poultry. 

Feeding  and  Management  of  Hogs. 

Some  Observations  on  the  Bulk  Hand- 
ling of  Grain  in  California. 

Announcement  of  the  California  State 
Dairy  Cow  Competition,  1916-18. 

Irrigation  Practice  in  Growing  Small 
Fruits  in  California. 

Bovine  Tuberculosis. 


